The present invention concerns a novel system for programming a device implanted in a patient from an external programming unit.
Microprocessor-based programmable cardiac pacemakers, which are implanted within the body of a patient, are in wide use today. These pacemakers can be communicated with from an external programmer, to alter the operating parameters of the implanted pacemaker. The pacemakers can be programmed to perform selected operations or to perform a telemetry function by returning information to the external programming device in a selected manner.
Some prior art programmable pacers are communicated with through a serial binary code format. Various transmission methods are used to transmit the binary code, such as magnetic reed switch, ultrasound, infrared signals, radio frequency pulses and bursts, amplitude modulation and frequency modulation.
The proper function of the communication link is of utmost importance to the operation of the pacer and ultimately to the well-being of the patient. There is a concern that the communication link may be affected by improper external sources, such as electromagnetic radiation emitted from various sources including therapeutic equipment. In addition, there may be improper interference from a programming code emitted by a programming device that is not intended to be used with the particular pacer that is implanted in the patient.
Certain prior art units include a reed switch enabling the programming circuit to operate. The reed switch operates as a simple switch which is closed by the application of a magnetic field. The reed switch is in the implant and an external magnet closes the switch to commence the operation. One method of programming is by external magnetic pulsations which force the reed switch to open and close to provide the data signals to the implant circuitry.
In U.S. Pat. No. 4,361,153, assigned to the assignee of the present invention, a system is described in which a carrier signal from the programmer is transmitted to a tank circuit in the implant. The tank circuit reflects back to the external programmer a wave formed with the signal data impressed thereon. The signal data is derived from a microprocessor which is coupled to sensors for various pacer functions such as rate, battery level, etc. If it is desired to change a function of the implanted pacer, the implant tank circuit acts as an antenna and receives the information. Instead of being reflected with signal data that is provided to the tank circuit, it is coupled to the microprocessor for providing the signals to the microprocessor which were received from the external programming circuit for making the desired change.
It is an object of the present invention to provide security so that the signal that is being transmitted from the external source to the implant is the proper signal from the external programming unit rather than some extraneous signal or rather than a signal from an improper programming unit.